Violet Red Bile Agar, 500 g (C08-0443-351)

Violet Red Bile Agar is recommended by APHA for the detection and enumeration of coliform organisms in water, milk, dairy and other food products (1,2). It is also recommended by BIS as a presumptive test solid medium for detection and estimation of coliform bacteria in food stuff (3). Druce et al (4) found this medium equally good as the indicator of coli-aerogenes in milk as MacConkey Broth. Recently, the agar formulation is recommended by ISO committee for the enumeration of coliforms (5). The medium is selective due to the presence of the inhibitors - bile salts and crystal violet. Crystal violet inhibits gram-positive microorganisms especially Staphylococci. Organisms which rapidly ferment lactose produce red colonies surrounded by redpurple halo (6). Lactose non-fermenters and late lactose fermenters produce pale colonies. Other related gram-negative bacteria can be suppressed by incubation at > 42°C or by anaerobic incubation. An overlay method is helpful to improve the specificity of the medium. Incubation may be carried out at > 42°C for 18 hours, 32°C for 24-48 hours or 4°C for 10 days depending on the temperature characteristics of the organisms to be recovered (7). Storage and Shelf-life: Store below 30°C in tightly closed container and the prepared medium at 2 - 8°C. Use before expiry date on the label. References: 1. Speck M. (Ed.), 1984, Compendium of Methods For The Microbiological Examination of Foods, 2nd ed. APHA, Washington, D.C. 2.Richardson G. (Ed.), 1985, Standard Methods for the Microbiological Examination of Dairy Products, 15th ed., APHA, Washington, D.C. 3.Bureau of Indian Standards, IS: 5401, 1969 (Second reprint - June 1990). 4.Druce R.G. et al, 1957, J. Appl. Bact., 20: 1. 5.International Organization for Standardization (ISO), 1991, Draft ISO/DIS 4832. 6.Davis J.G., 1951, Milk Testing, Dairy Industries Limited, London; pg 131 7.Mossel D.A.A. and Vega C.L., 1973, Hlth. Lab. Sci., 11:303.